1. Field of the Invention
This invention relates to a method of manufacturing a water-repelling film.
2. Description of the Related Art
As described in Japanese Patent Application Kokai Number 2002-38094, a water-repelling film has generally a contact angle of 140° or greater with respect to water. In Japanese Patent Application Kokai Numbers 2002-38094 and 10-259037, a method of manufacturing a water-repelling film by coating method is disclosed. According to the method, a substrate is coated with a coating liquid and then subject to heat-treatment at high temperature to provide the water-repelling film. The temperature for the heat-treatment is specified as 60° C. to 450° C. in Japanese Patent Application Kokai Number 2002-38094 and 400° C. to 600° C. in Japanese Patent Application Kokai Number 10-259037.
Also, as described in Japanese Patent Application Kokai Number 10-259037, the film is frequently subject to plasma discharge treatment to make the surface of the film rough or uneven so that the surface is activated to improve the function of the water-repelling film. The plasma discharge treatment is performed using plasma having an extremely high energy of several tens eV.
As described in the Non-patent Document Publication Number 45,566, titled “What is a high polymer material that repels water the most?” and written by Masamichi Morita, the contact angle of the water-repelling film depends upon the molecular structure and form of the surface of the water-repelling film. The molecular structure of a compound that forms the surface of the water-repelling film determines the free energy of the surface of the water-repelling film. According to the Non-patent Document, a film having many C—F and C—H bonds in its surface is of superior water repellency because of a low free energy of its surface. Moreover, according to the Non-patent Document, when the surface of the water-repelling film is made rough to have an enlarged surface area, the water repellency is further increased. That is, the water-repelling film is provided by the multiplier effect of the molecular structure and form of the surface of the film.
The water-repelling film can be used as a protection film for a semiconductor device because it repels water. However, if the water-repelling film is formed by the above-described coating method and the plasma discharge treatment, the semiconductor device receives damage. For example, the semiconductor device is damaged by the extension of a diffusion layer caused by high temperature heat-treatment in the coating method and/or charged particles contained in plasma of a high energy in the plasma discharge treatment.
In a Metal Oxide Semiconductor Field Effect Transistor (MOS FET) of a sophisticated semiconductor device of a fine pattern, the gate length is shorter and the diffusion layer, such as a channel is shallower in its depth and narrower in its width. Accordingly, the above-described damage is more critical problems to be solved.